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San Antonio Area Freeway System
PROJECT INFO: Wurzbach Pkwy at NW Military

This page last updated March 4, 2019

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Project locationLocation
Wurzbach Pkwy from Bluffton Oaks to Elm Creek

Status
Final planning

Description
This project will improve the Wurzbach Parkway intersections at NW Military and Lockhill-Selma.

At NW Military, the project will add a second dedicated left turn lane and convert the existing optional left/through lane to a dedicated through lane on all approaches, reconfigure all of the left turn movements to allow simultaneous opposing left turns, add a second right turn lane from westbound Wurzbach to northbound NW Military, and optimize the signals for the new configuration.

At Lockhill-Selma, the project will add an additional through lane for Wurzbach in both directions; the new westbound through lane will become a right-only lane at Elm Creek (i.e. through traffic will have to merge to the left to continue on Wurzbach.)

A previous proposal to build an underpass for Wurzbach at NW Military and a SPUI intersection was cancelled after public feedback (see history section below for more details.)

How this project will help
The additional lanes will provide additional capacity for turns and through traffic. At NW Military, re-orienting the left turn movements to allow for simultaneous operation will allow the left turns to be handled separately from the through movement. This will facilitate more efficient signal operation
because left turn green time can be terminated when the queue has emptied, thus allowing additional green time for opposing through traffic; the current intersection configuration and its inherent four-way signal operation does not permit this.

Timeline
This project is expected to start in Summer 2020 and should take about a year to complete.

Schematic
Click on the image below to open the detailed schematic for this project from TxDOT with my own annotations added to help clarify and explain the various elements. The schematic will open in a new window that you can scroll and zoom.

 
History
TxDOT always evaluates multiple options for any project to determine which alternative best addresses the need at the most reasonable cost. Normally, I don't present all the options studied for a project. For this project, however, I will because the option that provides the least improvement (especially long-term) was ultimately selected after the initial proposal was scuttled by opposition from adjacent neighborhoods. After an extended public-involvement process (and likely some behind-the-scenes political muscling), the project discussed above is what was finally accepted.

The original proposal presented to the public in 2016 was for a Single Point Urban Interchange (SPUI) at the NW Military intersection. This option would have built an underpass for through traffic on Wurzbach and would have configured the surface-level intersection as a SPUI. The primary opposition to this plan was that through traffic on the new access roads would not be possible. There is little need for through access roads at this location since the adjacent neighborhoods and shopping center have direct access onto NW Military, which facilitates any movements that would be lost by blocking through traffic on the access roads. But residents in the adjacent neighborhood deemed that too inconvenient, preferring instead to maintain their existing travel patterns at this intersection via their neighborhood access points on Wurzbach.

Given that, and an assortment of other objections posed by constituents regarding trees, downstream impacts at Lockhill-Selma, and various aspects of construction, TxDOT re-opened the evaluation process and proffered several other options for public consideration including several alternative intersection designsAfter several stakeholder meetings with those nearby HOAs and residents as well as the general public, the less-ambitious (and least effective) conventional improvements plan-- with some additional modifications-- was finally selected.

The options evaluated are listed below. A brief description along with an expected benefit rating (one to four plus ["+"] signs with four indicating the best overall improvement for traffic) and cost rating (one to four dollar signs ["$"] with four indicating the highest relative cost) are included for each. The projects are ordered generally from highest benefit to lowest. All of the options proposed the same changes to the Lockhill-Selma intersection and they were included in the final plan.

  • Single Point Urban Interchange (SPUI) [ ++++ | $$$$ ]
    As mentioned above, this was the original proposal for this project. An underpass for Wurzbach would have been built with exit and entrance ramps for NW Military. The signalized intersection on NW Military would have been configured as a SPUI with no through traffic on the Wurzbach access roads. For information on how a SPUI works and its benefits, see the alternative intersections page.




  • Modified SPUI [ +++ | $$$$ ]
    This is the same as the SPUI proposal above but with through lanes included on the access roads. Doing this decreases the signal efficiency since it requires an additional phase per cycle. With the same cost as a regular SPUI, the decreased efficiency of the signals caused the cost/benefit ratio for this option to drop appreciably.




  • Diverging Diamond Interchange (DDI) [ +++ | $$$ ]
    This option is similar to the SPUI option above but would have built a Diverging Diamond Interchange (DDI) similar to the one currently proposed for Blanco at Loop 1604 and Jones-Maltsberger at US 281 instead of a SPUI. As with the SPUI proposal, there would have been no through traffic on the Wurzbach access roads. For information on how a DDI works and its benefits, see the alternative intersections page.




  • Conventional diamond interchange/full underpass [ +++ | $$$ ]
    This plan would have built an underpass for Wurzbach through traffic and a conventional diamond interchange, i.e. the standard freeway/access road type interchange found everywhere. The four-phase signal operation for this type of interchange is the same as what is there today, but the decrease in traffic on the Wurzbach approaches provided by the underpass was still not enough to make this the most efficient option.




  • Conventional diamond interchange/partial underpass [ ++ | $$ ]
    This is the same plan as above except that only eastbound Wurzbach would have an underpass; westbound Wurzbach traffic would still go through the signalized intersection. This option was included to contrast with the previous option the impact on traffic at Lockhill-Selma. While it did decrease congestion there (because westbound traffic is "metered" here), it resulted in a very imbalanced signal operation here, which made it much less effective.




  • Displaced Left Turn (DLT) [ ++ | $$ ]
    This option would have built a displaced left turn intersection similar to the one currently under construction at Bandera and Loop 1604 and proposed for several other locations. Left turns from Wurzbach to NW Military would shift to the opposite side of the road upstream of the intersection. The through lanes on Wurzbach would be squeezed together in the existing median area to provide room for those left turn lanes.
    There would be no underpass in this plan. For information on how a DLT works and its benefits, see the alternative intersections page.




  • Median U-Turn (MUT, aka a "Michigan Left") [ + | $ ]
    This proposal would have eliminated left turns in all directions at the NW Military intersection. Instead, left-turning traffic would use new turnarounds constructed downstream on Wurzbach. This is similar to the "superstreet" intersections built in recent years at several locations around the area except that through traffic on Military would be allowed; this is instead known as a "Michigan Left" intersection. By eliminating left turns, the signals operate with just two phases, the most efficient operation available.
    For information on how a MUT works and its benefits, see the alternative intersections page.




  • Conventional intersection improvements [ + | $ ]
    This option only makes conventional improvements the existing at-grade intersection; it does not include an underpass. The plan shown below is the first proposal for the plan that was finally selected. This plan is different from the final proposal in the way it handles left turns from NW Military onto Wurzbach. In this plan, the intersection is not configured to allow for simultaneous left turns from NW Military; this reduces intersection efficiency. The final plan adds a second dedicated left turn lane for each direction of NW Military and utilizes the left turning configuration of a SPUI, thus allowing simultaneous left turns and wringing the most possible efficiency out of this plan. This proposal also adds a third through lane to both directions of Wurzbach, extends the right turn lanes, and adds a second right turn lane from westbound Wurzbach to northbound NW Military; these were all carried-through to the final plan.







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This page and all its contents are Copyright 2019 by Brian Purcell

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